1. Field of the Invention
This invention relates to alignment systems for manufacturing and more particularly to alignment marks employed on parts to be aligned.
2. Description of Related Art
The present invention relates to structures such as semiconductor devices with combination of an active region such as a silicon layer or a silicon substrate. On the silicon layer or substrate there are contact layers and polysilicon layers. During front end processing steps, usually both the polysilicon layers and contact layers are aligned to the active layer; and in such a case, there is a possibility for misalignment between the contact layer and the polysilicon layer. Many circuit designs, demand good alignment of the contact layers with both the active layer and the polysilicon layers. A nine (9) mark Field Image Alignment (FIA) marking system is employed in a system manufactured by Nikon Corporation in which alignment markings are provided on a work piece.
U.S. Pat. No. 4,962,318 of Nishi for "Alignment System for Exposure Apparatus", assigned to Nikon Corporation describes Field Image Alignment (FIA) markings at Col. 6, line 59 to Col. 7, line 61 and in FIG. 1A thereof. Light from a halogen lamp is directed onto an alignment mark. At Col. 10, line 15 to Col. 11, line 11, such an alignment marking is described as a pattern of stripes raised from the surface of a wafer covered with photoresist.
U.S. Pat. No. 5,808,910 of Irie et al., "Alignment Method" assigned to Nikon Corporation describes a Field Image Alignment (FIA) marking system at Col. 8, line 34 to Col. 9, line 7 and in FIG. 2 thereof.
U.S. Pat. No. 5,783,340 of Farino et al. "Method for Photolithographic Definition of Recessed Features on a Semiconductor Wafer Utilizing Auto-Focusing Alignment" discloses a method for forming an alignment marking formed a several marks in a trench for a stepper.
U.S. Pat. No. 5,401,691 of Caldwell "Method of Fabrication an Inverse Open Frame Alignment Mark" teaches a method of forming alignment marks.
U.S. Pat. No. 5,705,320 of Hsu et al. for "Recovery of Alignment Marks and Laser Marks after Chemical-Mechanical-Polishing" shows method steps for forming topographic alignment marks (topographical features or steps formed in a substrate) located in a window.